1. Field of the Invention
The present invention relates to a supercritical fluid chromatograph, and a liquid carbon dioxide delivery pump used by the same.
2. Description of the Related Art
A supercritical fluid chromatograph (SFC) uses a supercritical fluid as a mobile phase. A typical example of a supercritical fluid is supercritical carbon dioxide. Supercritical carbon dioxide is carbon dioxide at or above a critical temperature or a critical pressure. Supercritical fluid chromatography most often uses carbon dioxide because its critical pressure is 7.38 MPa, its critical temperature is, at 31.1° C., relatively close to a normal temperature, and it is non-flammable and chemically unreactive, and highly pure carbon dioxide may be obtained at a low cost. Supercritical carbon dioxide has properties that are desirable for chromatography, namely, low viscosity and high diffusivity. Compared to liquid chromatography, supercritical carbon dioxide chromatography is expected to achieve fast and more desirable separation.
Supercritical carbon dioxide is non-polar, and is similar to n-hexane, and thus, supercritical fluid chromatography that uses supercritical carbon dioxide as a mobile phase is basically normal chromatography, and is suitable for analysis of a non-polar compound. However, supercritical carbon dioxide is compatible with polar organic solvents such as methanol and ethanol, and by adding such a polar organic solvent as a modifier, the mobile phase may be polarized, and analysis of a polar compound is enabled. Accordingly, gradient analysis in which the added proportion of a modifier is gradually increased over time is also performed.
According to a supercritical fluid chromatograph that uses supercritical carbon dioxide, liquid carbon dioxide is delivered by being pressurized by a delivery pump. As the delivery pump, a plunger pump, for example, having a plunger that reciprocates inside a pump chamber is used. The delivery pump is used being cooled to a temperature below the critical temperature, such as 5° C., so as to perform delivery in a state of liquid carbon dioxide.
With the delivery pump, to prevent a rise in the temperature due to generation of heat during pressurization of liquid carbon dioxide, a heat exchange block is attached to a pump head, and a pipe from a cooling water circulation device installed outside the device is connected to cool the heat exchange block by cooling water, or a cooling device, such as a Peltier device, is attached to the heat exchange block to cool the block (see WO 2012/122361 A2).